Tube forming die



April 1o, 1945.

E. BERTALAN TUBE FORMING DIE 2 Sheets-Sheet 1 Filed Sept. 19, 1942 Willi/MMV l /NVENTOR '.sfRrALA/v April l0, 1945-. E, BERTALAN TUBE FORMNG DIE 2 Sheets-Sheet 2 'Filed Sept. 19, 1942 /N VEA/TOR E. BER TAL A N BY A T TOR/viv PQ# 5 vw insulating discs to pass therethroug Patented Apr. 1o, 1945 UNITED fsrlrrlzs PATENT oFFiE y l TUBE :Sltm mit a I Application September 19, 1942, Serial No. 459,047

8'Claims.

This invention relates to tube forming dies and particularly t dies for forming tubular outer conductors of coaxial cables.

One type of coaxial cable used commercially comprises a small central conductor in the form of'a wire, an outer tubular conductor and a plurality of slotted discs positioned upon the central conductor for the dual purpose of insulating the conductors from each other and spacing the conductors so that their axes are coincident. The

outer tubular conductor employed in such cables l is formed from a tape made of copper orother suitable conducting material and the edges of the tape are provided with spaced serrations that are bent away from the plane of the tape. When this tape is formed into a tube, the serrations .are flattened down on. the outside of the tube so that they overlap the abutting edges of the tape and serve to hold the tube together.

To meet the rigid electrical requirements for coaxial cables used in communication equipment, it is necessary that the conductors be of uniform size and conguration and that they be uniformly spaced. Hence, it is essential that the tubular conductors used in such cables be of uniform diameter so as to present smooth inner and outer surfaces and that the serrations be uniformly, yet rmly, pressed into position to lock the tubular conductor in-its finished shape.

'I'he object of this invention is to provide tubeforming dies by means of which tubes of uniform dimensions and configurations may be made.

In accordance with one embodiment of the invention, there is provided a tube-forming die.

comprising a body member having an elongated converging tube-forming opening formed centrally thereof and having a groove formed therein communicating with the tube-forming opening to permit a central conductor provided with spaced 'Ihe invention will be clearly understood from the following detailed description 'of la speciflc embodimentthereof, when read in conjunction with the accompanying drawings, in which Fig. 1 is a side elevational view of a tube-forming die embodying the invention; FiFig. 2 is a top plan view of the die shown in Fig. 3 is a vertical sectional'view taken on line '3 3 of Fig. 1;

view taken Online Fig. 8 is a `vertical Isectional view taken on line 8 8 of Fig. 1;

Fig. 9 is a vertical sectional view taken on line 9 9 of Fig. 1; A

Fig. 10 is an enlarged vertical sectional view of the forming die shown in Fig. 2, the section being taken on line Ill-I0 of that figure;

Fig. 11 is an enlarged top plan view of a tubeforming element forming a part of the apparatus;v

Fig. rl2 is an enlarged bottom plan view of another tube-forming element forming a part of the apparatus, and

Fig. 13 is an enlarged sectional view taken on line |3 |3 of Fig. 1.

Referring now to the drawings, wherein like reference numerals are employed to designate like parts throughout the several views, a tube-forming die is disclosed which comprises a lower die section and an upper die section 2| which are secured in operative position by means of bolts 23-23 and dowel` pins 24 24. The assembled tube-forming die is secured to a support 26 by The lower die section 20 consists of two segments 30 3|l which are secured together by bolts 3| 3I so as toA form a unitary element. A forming surface 33 (Figrll) is provided substantially centrally of the die section 20, and at the sides of the forming surface 33 there are provided a pair of grooves 34 34, the purpose of which will be more fully explained hereinafter.

The` forming surface 33 converges from the left end thereof, as seen in Fig. 11. toward the right endv thereof and gradually changes from a rectangular shaped groove 36 at the left end thereof into a. circular opening 31 ai; the right end thereof. During its transposition from the rectangular groove 36 to the circular opening 31, the forming surface 33 -follows substantially the shape naturally assumed by a paper tape which is the same width as the metal tape to be formed into a tube and which is rolled into a tube at one end and allowed to open out fiat at the other end. The grooves 34-34 converge and also rise as they extend away from the left end of the forming surface 33,` as seen in Fig. 11, and join into a single groove 38 at the top of the circular opening 3l.

Fig. 6 is a vertical sectional view taken on line y 6 6 of Fig. 1;

. Fig. 7 is a vertical sectional view taken on line 1 1 of Fig. 1;

Except for the grooves 34-34 and 38, the forming surface 33 is smooth andy offers slight resistance to the passage of a metallic tape thereover as the tape is being formed thereby into a tube.

The upper die section 2| consists of a rectangular block 40 having formed thereon a projection 4| provided with av central longitudinal groove 42 having a dared end 44. The outer surface 45 of the projection 4| constitutes a formin'g surface which coacts withv the forming 'surface 33 in the die section 20 to provide a thin tube-forming opening 4-6 (Figs. 4, 5 and 6) the 41-41 to the right hand end of the die section 20, as seen in Fig. 1, for the purpose of insuring exact roundness in a tube formed in the tubeforming die. The die 48 resembles a wire-drawing die and is provided with a hard insert 49 made of a suitable wear resistant material, such as tungsten carbide, in which is formed a forming opening 50 which is in alignment with the circular opening 31 in the die section 20. In the upper portion of the opening 50 there is formed a groove 5I which is in alignment with and forms a continuation of the groove 38 in the opening 31. The shaping die 48 acts in somewhat the same manner as a wire-drawing die to shape the tube in circular form.

In the operation of the tube forming die, the segments 30-30 of the lower die section 20 are securely fastened together by means of the bolts 3|3|, and the upper die section 2| is positioned above the lower die section 20 and held in position by means of the bolts 23-23 and dowel pins 24-24. The two die sections, when secured in operative position, act as a unitary body member and are so described in the annexed claims. A central coaxial cable conductor 52, having spacedly positioned thereon a plurality of insulating discs 53-53, and a metallic tape 54, provided with serrations 56-56 along the edges thereof, are drawn through the tube-forming die by any suitshown).

It will be evident from an examination of Fig. 3 that the serrations 58`58 formed on the edges of the tape 54 project downwardly andthen outwardly in a plane parallel to the plane of the tape, and that prior to its entering into the forming die the tape A54 is flat. Since the groove 36 of the forming surface 33 is rectangular in cross section, the tape 54 lies at upon the bottom thereof and enters freely the forming opening 46. As the tape and the central conductor are advanced through the forming die, the central conductor and the discs 53-53 carried thereby enter the groove 42 in the projection 4I,-as shown in Fig. 4, the flared portion 44 of the groove 42 serving to guide the discs 53-53 into the opening 42. Meanwhile the tape 54 enters the forming opening 46, while the serrations 56-55 on the tape enter the grooves 34-34.

As the tape continues its advance through the forming die, it is caused by the forming opening 46 to gradually assume a circular shape (see Figs. 4, 5, 6, '7, 8 and 9) and to surround the central conductor and the insulating discs. When it enters the circular opening 31, the edges of the tape have been caused to abut one another, while the serrations 56-56 which have been advancing along the converging and rising grooves 34-34 have been caused to overlap these abutting edges in the manner shown in Fig. 8. Since the overlapping serrations 56-53 extend beyond the exterior surface of the resulting tube, the groove 38 into which thevgrooves 34-34 lead is provided for the purpose ofreceiving the overlapping serrations andl for forcing them into close engagement with the formed tube.

If the tube which emerges from the circular -able means suchas a power driven capstan (not 4 opening 31 is not completely circular in cross section, it is converted into a circular tube by the shaping die 48. As the resulting tube is advanced through the opening 50, the overlapping serrations 58-56 are engaged by .the groove 6l, which is of such dimensions that the serrations are pressed tightly against the adjacent portions oi the formed tube, thereby insuring a close engagement between the serrations and those portions of the tube which they overlap. It is obvious that when the opening 50 and the groove 5i in the hard insert 49 forming part of the shaping die 63 become worn, the hard insert 49 may be replaced by another insert having the proper dimensions. Thev coaxial cable unit which results from this operation is shown in cross section in Fig. 13 and consists of the central conductor 52, an external tubularr conductor formed from the tape 5d, and the interposed discs 53-53. The tubular conductor is held in its desired shape and position by means of the overlapping serrations Sii-'56. The units produced by means of a tube-forming die of the type described and illustrated are of uniform size and shape, and the external conductors are substantially circular in cross section. As a result such units have the uniformity and symmetry needed to provide satisfactory conductors` for coaxial cables used in communication circuits.

It would be difficult to form a surface having the intricate contour of the forming surface @il in a solid block of metal.- Consequently, the lower die section is formed of two segments 303 and the right and left hand halves .of the forming surface 33 are formed in the respective segments.

Before the complete die is assembled, the segments 30-30 are assembled and held in position by means of the bolts 3l-3I so that they in effect constitute a single die section.

Due to the smoothness of the forming surfaces 33 and 45 and the fact that the forming opening 4B provided therebetween follows the shape naturally assumed by a paper tape that is freely rolled into a tube, these dies will form a metallic tape into a tube without undue or uneven strain on the metal and with the use of a relatively small amount of power. Hence, it will be evident from the foregoing description that the tubeforming dies embodying this invention provide a means by which coaxial cable units may be rapidly formed without the expenditure of excessive power, and that the units so formed are suiciently uniform to meet commercial requirements for coaxial cable conductors.

What is claimed is:

1. A die for forming a tube from a metal tape having serrated edges, which comprises a body member having formed therein an elongated converging tube-forming surface and a pair of grooves for receiving the serrations on the edges of the tape, said grooves converging to form a single groove which receives the serrations after they have been caused to overlap the abutting edges of a tube formed by the tube-forming surface and serves to press the serrations into close contact with the abutting portions of the tube.

2. A die for forming a metal tape having serrated edges into a tube about a conductor having spaced insulating discs mounted thereon, which comprises a body member having formed thereon a converging tube-forming surface and having a groove to receive the conductor and insulating discs about which the tape is formed linto a tube,

on the edges of the tape, said pair of grooves converging to form a single groove which receives the serrations and presses them into close contact with the abutting portions of a tube formed bythe tube-forming surface, and a shaping die associated with the body member for insuring a circucomprises an elongated die section provided withv a forming groove which gradually changes from an open rectangle at the entrance end to a tubular passage at the exit end thereof, and a, companion die section having projecting therefrom a forming surface which extends into the open portion of the groove in the first mentioned die section and which changes in' contour so as to correspond to the adjacent surface of the groove, whereby there is provided a narrow curved tubeforming passage of uniform thickness, said first mentioned die section having a" groove formed therein adjacent to one edge of the forming groove and then extending parallel to the axis of the tubular passage, which groove extends the entire `length of the die section along the path followed by the serrations on the edge of a tape when the tape is drawn through the die section to provide clearance for the serrations and is shallow enough at the exit end of the tubular passage in the die section to press the serrations into` close contactwith the abutting portion of-a tube formed by the tube-forming opening.

4. A die for forming a tube from a metal tape having onset separations on the edges thereof, which comprises an elongated die section having formed longitudinally thereof a forming surface which gradually changes in contour from a plane formed by the bottom of a rectangular groove to a circular passage, a companion die section having formed thereon a projecting forming surface one edge of the tape over the other edge of thev extending into a portion of the grooved part-of and adjacent to the first mentioned forming surfaceand corresponding in contour to theadjacent portion of the nrst mentioned forming surface, whereby the die sections coact to provide a narrow curved tube-forming passage of uniform thickness, and a shaping die positioned adjacent to the exit end of the circular passage to shape a tube formed from a tape drawn through the circular passage, said first mentioned die section having a pair of grooves extending along the' edges of the tube-forming surface from the beginning of the rectangular groove to the circular passage where they merge, extend parallel to the circular passage, and become suiciently shallow to press the offset serrations of the tape into close contact with abutting edges of the tape as the edges of the tape are brought into abutting relationship by the tube-forming surfaces.

5. A die for forming a tube from a metal tape having offset serrations along an edge thereof, which comprises a die section having an elongated forming surface formed therein that is fiat at the entrance end thereof and gradually converges to a circular passage at the exit end thereof, whereby a tape drawn over the forming surface is formed into a tube with its edges in abutedge of such tape until the serrations reach the circular passage and becoming shallow enough in the circular passage to press the serrations on the one edge of the tape over the other edge of the tape when the tape is drawn through the passage. l

6. A die for forming a tube from a metal tape having offset serrations on an edge thereof, which comprises a die section having a forming surface formed therein that is iiat at the entrance end thereof and gradually converges to a circular passage at the exit en/d thereof, whereby a tape drawn over the forming surface is formed into a tube with its edges in'abutment, said die section being provided with a rectangular groove extending helically along one edge of the forming surface `until it reaches the entrance end of the circular passage and then extending longitudinally of and in communication with the passage, the cross-sectional area of said groove being substantially con stant in the portion of the groove up to the entrance end of the circular passage and then decreasing to the exit end of the circular passage, whereby the groove serves to provide clearance for the offset serrations formed on the edge of such tape until the serrations reach the circular passage and then presses the offset serrations on the tape when the tape is drawn through the passage.

7. A die for forming tubes from metal tapes having serrations along at least one edge thereof, which comprises an elongated member having a forming surface formed therein which gradually changes from a flat portion at one end thereof to a concave, semi-cylindrical portion at the other end thereof, a second member having formed thereon a forming surface complementary to the rst mentioned forming surface, and means for vsecuring the members together with the edges of the forming surfaces in abutting positions so that the nat portions of the forming surface form a plane and the remaining portions gradually converge to a cylindrical passage formed by the semicylindrical portions, atleast one of said members being provided with a groove beginning at the edge of the fiat portion of the forming surface of that member until it is inverted at the entranceend of the cylindrical passage and then continues parallel to the passage and gradually diminishes in cross-sectional area, whereby the offset serrations on the tape are provided with clearance until the tape reaches the entrance end of the passage and the serrations are pressed over kthe abutting edge of the tape as the tape is drawn through the passage.

8. A die for forming a metal tape having serrated edges into a tube about a conductor having spaced insulating discs mounted thereon, which comprises a body member having formed thereon ment, said die section being provided with a` groove extending helically along one edge of the forming surface until it reaches the entrance end of the circular passage and then extending longitudinally` of and in communication with the passage, said groove being deep enough to provide clearance for the offset serrations formed on the a convex converging tube-forming surface and having a groove to receive the conductor and insulating discs about which the tape is formed in`to a tube, and a companion body member having formed therein-an'elongated concavely converging tube-forming surface for cooperating with the convex surface to form the tape into a tube around the conductor and the insulating discs and also being provided with a pair of grooves for receiving the serrations on the edges of the tape. said pair ofgrooves converging to form a single .groove which receives the serrations and presses them into close contact-,with the abutting portions of the tube formed by the tube-forming surfaces.

EDWARD BERTALAN. 

